The thermal performance of heating and cooling systems is strongly influenced by the heat exchanger performance. It is important to assess the performance and characteristics of crossflow heat exchangers in transient situation, especially when a sudden change in their operating conditions takes place. This research advances the understanding of transient heat transfer in an unmixedunmixed serpentine minichannel heat exchanger with the aim of improving heat transfer and exploring transient response. The transient behaviour of the crossflow minichannel heat exchanger for perturbations in hot fluid mass flow rate are investigated. Variations in the hot fluid (water) mass flow rate starting from an original value of 20 / to the subsequent steps of 0.5, 0.8, 1.5, 2.0, 2.5 and 3.0 are considered. The hot fluid inlet temperature of 70℃ and cold fluid (air) inlet temperature of 13℃ and velocity of 6 / are maintained throughout the simulations for all the mass flow steps. This study uses threedimensional computational models to resolve flow and heat transfer in the liquid-to-air crossflow heat exchanger. ANSYS FLUENT, a finite volume method based computational fluid dynamics code, is used to perform the numerical simulations. Models are validated with the transient experimental results available in scientific literatures to represent the real-world applications. Very good agreements in numerical predictions are achieved for the model. Various temperature response and heat transfer profiles in the minichannel heat exchanger were obtained. Faster response time is observed for higher step predicted from 4084 2 ⁄ to 8356 2 ⁄ for the hot fluid Reynolds number of 950 ≤ ℎ ≤ 2265. New correlations for the dimensionless transient outlet temperature and the transient Nusselt number of hot fluid in the forms of ℎ, * () = ℎ, * (∞){1 − 1 − 1 * } and ℎ () = ℎ (∞){1 + 2 − 2 * }, respectively are developed. These correlations can be useful sources for future researchers working on minichannel heat exchanger as their application becomes more widespread.